The present invention relates generally to filtration devices and more particularly to microfabricated filters constructed with substrate structures. The present invention further relates to containment capsules for immunological isolation of cell transplants that are constructed with substrate structures.
Filtration devices are an indispensable necessity, for example, in the health care industry. Within the health care industry, accurate filtration devices are required, for example, in the fields of pharmaceutical technology, biotechnology, bioseparation, which includes plasma fractionation, and diagnostics. For many applications within these areas, required filtration device features include: precise control of pore size and distribution, absolute pore size as small as the nanometer range, chemical inertness, high mechanical strength, high throughput, and a simple microfabrication process.
Precise control of filter pore sizes down to the 20 nanometer (nm) range would allow biologically important molecules to be mechanically separated on the basis of size. For example, such pore sizes may be used to achieve the heretofore elusive goal of viral elimination from biological fluids. In such absolute filtration applications, the presence of even one unwanted particle could be deleterious.
Microfabricated filters are known in the art to possess such pore sizes. For example, a microfabricated filter comprised of thin film structures is described in co-pending U.S. patent application Ser. No. 08/207,457, entitled "MICROFABRICATED PARTICLE FILTER", filed on Mar. 7, 1994, now U.S. Pat. No. 5,651,900, and assigned to the assignee of the subject application. This filter yields tightly controlled pore sizes and distributions, with a pore width as small as 5 nm. The filtration channels of the filter are entirely composed of polycrystalline silicon (polysilicon).
A microfabricated filter comprised of a combination of substrate and thin film structures is described by Kittilsland et al. in Sensors and Actuators, A21-A23 (1990) pp. 904-907. This filter yields a pore width as small as 50 nm. The filtration channels of this filter are composed of a combination of polysilicon and single crystalline silicon.
Another microfabricated filter that is comprised of a combination of substrate and thin film structures is described in co-pending U.S. patent application Ser. No. 08/663,644, entitled "MICROFABRICATED FILTER WITH SPECIALLY CONSTRUCTED CHANNEL WALLS, AND CONTAINMENT WELL AND CAPSULE CONSTRUCTED WITH SUCH FILTERS", filed on Jun. 14, 1996, now U.S. Pat. No. 5,798,042, and assigned to the assignee of the subject application. This filter has a pore width as small as 5 nm. The filtration channels of this filter are also composed of a combination of polysilicon and single crystalline silicon.
A microfabricated filter that is constructed from silicon devices bonded to a glass plate is described by Brody et al. in "A Planar Microfabricated Fluid Filter," Transducers '95, 779-782, 1995. The pores of the filter are defined by spaces formed between barriers etched in the silicon devices and the glass plate. The width of the pores are thus determined by the etch rate of silicon. This filter has been demonstrated to remove 16 micrometer (.mu.m) particles from a fluid.